Many processing plants, such as refineries, chemical plants, and electric power generation plants, use networks of pipelines. Failure of these pipelines can cause major disruption of plant operation and an unscheduled outage. To ensure safe operation of such plants, there is a need for on-line non destructive testing methods to inspect and monitor pipelines.
One effective method for inspecting and monitoring a long length of pipelines is guided wave testing (GWT) using a magnetostrictive transducer (MsT). A common implementation of this method uses primarily torsional waves (T-waves) that are generated in a thin ferromagnetic strip placed around or in the pipe under test. MsT testing can also be achieved with direct generation of waves in the tested structure via electromagnetic force.
The generated waves propagate along the pipe and are partially reflected by geometric irregularities present in the pipeline, such as welds or corrosion defects. The reflected signals are then detected in a pulse-echo mode. From the arrival time of the reflected signal and the signal amplitude, the axial location of the irregularity and its severity are determined. In above-ground pipelines, this method can detect 2% to 3% defects over 500 feet from a sensor location. The % refers to the defect's cross-sectional area relative to the total cross section of the pipe wall.